In general, when fabricating patterned-mirror, or ridge-guide, VCSELs, a first mirror stack is epitaxially deposited on the surface of a substrate, followed by an active region and then a second mirror stack. The second, or upper, mirror stack is etched to form a mesa (ridge) which essentially defines a waveguide in which the lasing occurs. The major problem in this fabrication scheme is that etching the second mirror stack is a very complicated and critical step. Much care must be used not to inadvertently etch into the active region and, thereby, reduce the reliability of the device. In many fabrication processes this etch step is controlled only by timing and careful control of the etch rate. Also, this process causes difficulties with control of the patterned mirror height and uniformity across the wafer (generally thousands of VCSELs are formed on a single wafer).
In a U.S. Pat. No. 5,293,392, entitled "Top Emitting VCSEL with Etch Stop Layer", issued Mar. 8, 1994 an etch stop layer is grown in the second, or upper, mirror stack and utilized to automatically stop the etch at a desired level. While the etch stop method utilizes the excellent control achieved in MOVPE growth to define the patterned mirror height, the growth of a layer of dissimilar material (the etch stop layer) is required which can significantly complicate the fabrication process.
Accordingly, it is desirable to provide a fabrication method which solves the above described problems.
It is a purpose of the present invention to provide a new and improved method of fabricating patterned-mirror VCSELs.
It is another purpose of the present invention to provide a new and improved method of fabricating patterned-mirror VCSELs wherein complicated etching steps are not required.
It is still another purpose of the present invention to provide a new and improved method of fabricating patterned-mirror VCSELs utilizing selective growth techniques.